'Umar ibn 'Abdu'l-'Aziz asked Abu Bakr ibn Abi Hathama, "Why did
Abu Bakr write, 'From Abu Bakr, the Khalifa (Successor) of the Messenger
of Allah' and then 'Umar wrote after him, 'From 'Umar ibn al-Khattab, the
khalifa (successor) of Abu Bakr'? Who was the first to write 'the Amir
al-Mu'minin'?" He replied, "My grandmother, ash-Shifa', related to me,
and she was one of the first to write 'the Amir al-Mu'minin'?" He said,
"My grandfather, ash-Shifa' related to me, (and she was one of the first
Muhajirun and when 'Umar ibn al-Khattab entered the market, he visited
her), saying, ''Umar ibn al-Khattab wrote to the governor of Iraq requesting
him to send him two trustworthy noble men so that he could question them
about Iraq and its people. He sent him a master of Iraq, Labid ibn Rabi'a
and also 'Adi ibn Hatim, and they came to Madina. They made their camels
kneel in the courtyard of the mosque, entered it and found 'Amr ibn al-'As.
They said to him, ''Amr, ask permission for us to visit the Amir al-Mu'minin,
'Umar.' 'Amr got up and went to 'Umar. He said, 'Peace be upon you, Amir
al-Mu'minin.' 'Umar said to him, 'Ibn al-'As, what made you use this name?
You have deviated from what you normally say.' He said, 'Yes, Labid ibn
Rabi'a and 'Adi ibn Hatim came and said to me, "Ask permission for us to
visit the Amir al-Mu'minin." I said, "You two, by Allah, have hit upon
the correct name. He is the amir and we are the believers."' The title
originated on that day."